It is common practice to mix particulate solids, liquids and gases with motionless mixers, having, as the name implies, no moving parts. Mixers of this category consist of baffles of various types arranged sequentially in a tube or pipe. As a process of division and recombination, separate input components can be mixed or dispersed within one another at the output of said tube or pipe. Difficulties are often experienced, however, when mixing materials of widely disparate viscosities and/or very different flow rates. For example, in the polymer field, it is at times desirable to mix very small quantities of a low-viscosity material within a much larger quantity of a high-viscosity material. When this is done, the low-viscosity material tends to tunnel through the mixing element without blending with the high viscosity material to any great extent.
It is well known that one of the mechanisms that allow for the mixing of fluids is diffusion. However, when dealing with high-viscosity materials which typically produce laminar flow, diffusion rates are very small. It is known that the rate of mass transfer (N) of the diffusing component measured in moles per second, per unit area, is equal to the diffusivity (D) multiplied by the local concentration gradient (dC/dR). Thus, since (D) is small in high-viscosity material, it is necessary to make the concentration gradient dC/dR large in order to maximize the value of the mass transfer rate.
One common industrial solution to this mixing problem is to pre-mix the additive with some of the main product before injection into the main mixer line. Although this approach is helpful, it adds considerably to the complexity of the operation.
It is thus an object of the present invention to provide a device which is capable of mixing materials having widely disparate viscosities and/or very different flow rates.
It is a further object of the present invention to provide a device which can effectively pre-mix two components of a fluid stream and feed the pre-mixture to a main mixing apparatus to improve the overall efficiency of the mixing system.